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Does this SEPIC LED driver have poor phase margin?

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Flyback

Well-Known Member
Hello,
Does this 5W SEPIC LED driver have a poor phase margin.?
The LED current oscillates at ~500Hz (loop crossover frequency) during start-up, as it rises upwards, -however, there is absolutely no LED current overshoot, and the LED current never oscillates when it gets near its regulation value of 50mA.

The LED driver spec is:
Vin = 12V
Vout = ~97V
I(LED) = 50mA
Constant off time
Fsw = 88KHz when in regulation (50mA)

Attached is the schematic ,LTspice simulation, and waveform of LED current and output voltage at start-up
 

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  • SEPIC LED driver 50mA.pdf
    56.3 KB · Views: 667
  • LED current in blue_Vout in green.jpg
    LED current in blue_Vout in green.jpg
    53 KB · Views: 152
  • _SEPIC LED driver 50mA.asc
    11.8 KB · Views: 161
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